A standard motor-vehicle drive system has a combustion engine connected via a clutch to a multispeed transmission that in turn drives the load constituted by the vehicle wheels. It is known to provide an electronic controller that is fed inputs corresponding to engine speed, road speed, and transmission setting, and that also itself stores the operating characteristics of the engine and transmission, so that this controller can display and even effect the necessary gear changes. Such a fully automatic system rarely gives satisfactory performance because the shifting cannot be tailored to particular circumstances, for instance an impending stop that would contraindicate an upshift or icy road conditions that would be most safely navigated in a higher gear.
Accordingly semiautomatic drive systems are known. In the EPS system of Daimler-Benz which is used with a 16-speed bus transmission the shift lever does not act directly on the transmission. Instead it can be shifted forward in a slot for upshifting and backward for downshifting, and a display indicates which gear the transmission is in currently. Thus to upshift two gears the lever is pushed forward twice. The driver operates the clutch manually in the conventional manner.
The AVS system of Zahnradfabrik Friedrichshafen has a controller which calculates and displays what gear the vehicle should be traveling in, given engine characteristics, desired road speed (as determined by accelerator-pedal position), and transmission characteristics. The driver can opt for the indicated preferred gear and select it by manual operation of the clutch, or operate a switch and select another gear.
In European patent application 0170465 A of Eaton a so-called SAMT drive is shown which displays, in addition to the currently selected gear, whatever higher and lower gears are still permissible, taking into account maximum and minimum engine speeds and road speed. In this arrangement the clutch is only operated manually for starting from a stop; once rolling the clutch operates automatically.